Jig saws can incorporate a pendular stroke device for generating an additional feed movement of the saw blade. This combined with the reciprocating movement of the saw blade causes the saw blade to move around an orbital path. At times it is desirable to eliminate the component of pendular movement of the saw blade so that the saw blade only performs a reciprocating movement.
United Kingdom Patent Specification No. 1,093,032 proposes a mechanism for both eliminating and adjusting the amplitude of such pendular movement. To generate this pendular stroke movement, a leg of an oscillated U-shaped pendular element is caused to engage with one end of a pivotally mounted bell crank lever that carries at its other end a support roller that engages the saw blade. As a result of the oscillating movement of the pendular element, the bell crank and the support roller are pivoted around a bearing shaft of the bell crank so that the support roller superimposes the additional feed movement upon the reciprocating saw blade.
In order to eliminate the effect of the pendular stroke in U.K. Pat. No. 1,093,032, the leg of the bell crank lever acted upon by the pendular element is pivoted by engagement with a rotatable stop out of engagement with the pendular element. The result is that, due to this pivotal position of the bell crank lever, the support roller is forced against the saw blade and moves the latter into an oblique position with respect to the shoe of the jig saw. Such an oblique position is disadvantageous, particularly if the jig saw is to make a circular cut in a workpiece, because no accurate guidance along the desired path of cut is then possible.
It has been proposed in U.S. Pat. No. 4,137,632 to generate the feed movement of the saw blade of a jig saw by means of a rotating cam disc whose center axis extends substantially in the direction of the feed movement of the saw blade and which has an annular engagement surface that is situated at least in part in a plane oriented obliquely to the center axis. By means of this engaging surface provided on the cam disc, the lower bearing of the saw blade holder is displaced to such an extent upon rotation of the cam disc that the desired feed movement of the saw blade is generated. Although this jig saw is admittedly of simple design, nevertheless it does not readily permit the use of a support roller or the like for generating the pendular stroke movement and supporting and guiding the saw blade.